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United States Patent |
6,002,241
|
Jacobs
,   et al.
|
December 14, 1999
|
Dual mode split-boost converter and method of operation thereof
Abstract
A split-boost converter having a main inductor, first and second main
switches and floating and fixed outputs and a method of operating the
same. In one embodiment, the converter includes an auxiliary diode coupled
between the main inductor and a first rail of the floating output, and an
auxiliary switch coupled to a node between the main inductor and the
auxiliary diode and a second rail of the floating output. The converter is
operable in a first mode, when an input voltage of the converter at least
equals an output voltage of the converter, in which the auxiliary switch
remains open and the first and second main switches are modulated to
operate the converter. The converter is further operable in a second mode,
when an input voltage of the converter is less than an output voltage of
the converter, in which the first and second main switches remain closed
and the auxiliary switch is modulated to operate the converter.
Inventors:
|
Jacobs; Mark E. (Dallas, TX);
Jiang; Yimin (Plano, TX);
Mao; Hengchun (Plano, TX)
|
Assignee:
|
Lucent Technologies Inc. (Murray Hill, NJ)
|
Appl. No.:
|
183076 |
Filed:
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October 30, 1998 |
Current U.S. Class: |
323/225; 307/44 |
Intern'l Class: |
G05F 001/613 |
Field of Search: |
307/44,45
363/61
323/222,225
|
References Cited
U.S. Patent Documents
5701096 | Dec., 1997 | Higashiho | 327/536.
|
Other References
"A New Control Scheme for Buck+Boost Power Factor Correction Circuit" by Y.
Jiang and F. C. Lee; 1993; pp. 189-193.
"Three-Level Boost Converter for and its Application in Single-Phase Power
Factor Correction" by Y. Jiang and F. C. Lee; 1994; pp. 127-133.
"An Improved High-Efficiency Rectifier for Telecom Applications" by M. E.
Jacobs, R. W. Farrington, G. H. Fasullo, Y. Jiang, R. J. Murphy, V. J.
Thottuvelil, K. J. Timm: 1996; pp. 530-535.
"Analysis and Design of a Wide Input Range Power Factor Correction Circuit
for Three-Phase Applications" by Ray Ridley, Siegfried Kern and Berthold
Fuld; 1993; pp. 299-305.
|
Primary Examiner: Riley; Shawn
Claims
What is claimed is:
1. A split-boost converter having a main inductor, first and second main
switches, floating and fixed outputs and comprising:
an auxiliary diode coupled between said main inductor and a first rail of
said floating output; and
an auxiliary switch coupled to a node between said main inductor and said
auxiliary diode and a second rail of said floating output, said converter
operable in:
a first mode, realized when an input voltage of said converter at least
equals an output voltage of said converter, in which said auxiliary switch
remains open and said first and second main switches are modulated to
operate said converter, and
a second mode, realized when an input voltage of said converter is less
than an output voltage of said converter, in which said first and second
main switches remain closed and said auxiliary switch is modulated to
operate said converter.
2. The converter as recited in claim 1 further comprising a first capacitor
coupled across said first and second rails.
3. The converter as recited in claim 1 further comprising a second
capacitor coupled across first and second rails of said fixed input.
4. The converter as recited in claim 1 further comprising a single-phase
rectifier coupled to said main inductor.
5. The converter as recited in claim 1 further comprising a main diode
coupled between said second rail and a first rail of said fixed output.
6. The converter as recited in claim 1 wherein said first mode is realized
when said input voltage at least equals said output voltage of said
converter and at most equals twice said output voltage.
7. The converter as recited in claim 1 wherein said output voltage is
between about 350 volts and about 400 volts DC.
8. A method of operating a split-boost converter having a main inductor,
first and second main switches and floating and fixed outputs, comprising:
connecting an auxiliary diode coupled between said main inductor and a
first rail of said floating output;
operating said converter in a first mode, when an input voltage of said
converter at least equals an output voltage of said converter, in which an
auxiliary switch coupled to a node between said main inductor and said
auxiliary diode and a second rail of said floating output remains open and
said first and second main switches are modulated to operate said
converter; and
operating said converter in a second mode, when an input voltage of said
converter is less than an output voltage of said converter, in which said
first and second main switches remain closed and said auxiliary switch is
modulated to operate said converter.
9. The method as recited in claim 8 further comprising charging a first
capacitor coupled across said first and second rails.
10. The method as recited in claim 8 further comprising charging a second
capacitor coupled across first and second rails of said fixed input.
11. The method as recited in claim 8 further comprising providing said
input voltage with a single-phase rectifier coupled to said main inductor.
12. The method as recited in claim 8 further comprising forward-biasing a
main diode coupled between said second rail and a first rail of said fixed
output.
13. The method as recited in claim 8 wherein said first mode is realized
when said input voltage at least equals said output voltage of said
converter and at most equals twice said output voltage.
14. The method as recited in claim 8 wherein said output voltage is between
about 350 volts and about 400 volts DC.
15. A split-boost converter, comprising:
a main inductor;
first and second main switches coupled to said main inductor;
floating and fixed outputs to said first and second main switches and
having respective first and second rails;
first and second capacitors coupled across said first and second rails of
said floating and fixed outputs, respectively;
an auxiliary diode coupled between said main inductor and said first rail
of said floating output; and
an auxiliary switch coupled to a node between said main inductor and said
auxiliary diode and said second rail of said floating output, said
converter operable in:
a first mode, realized when an input voltage of said converter at least
equals an output voltage of said converter, in which said auxiliary switch
remains open and said first and second main switches are modulated to
operate said converter, and
a second mode, realized when an input voltage of said converter is less
than an output voltage of said converter, in which said first and second
main switches remain closed and said auxiliary switch is modulated to
operate said converter.
16. The converter as recited in claim 15 further comprising a single-phase
rectifier coupled to said main inductor.
17. The converter as recited in claim 15 further comprising a main diode
coupled between said second rail and a first rail of said fixed output.
18. The converter as recited in claim 15 wherein said first mode is
realized when said input voltage at least equals said output voltage of
said converter and at most equals twice said output voltage.
19. The converter as recited in claim 15 wherein said output voltage is
between about 350 volts and about 400 volts DC.
20. The converter as recited in claim 15 wherein said output voltage is
about 400 volts DC.
Description
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to power conversion and,
more specifically, to a split-boost converter that adapts its switching to
different ranges of input voltage and a method of operating the same.
BACKGROUND OF THE INVENTION
Boost converters have been widely used in various power conversion
applications employing both three-phase and single-phase AC input
voltages. The conventional single-switch boost converter has become the
most popular topology for single-phase power factor correction. For an RMS
AC input voltage in the range of 85 volts to 265 volts, a boost technology
can provide a sinusoidal input current and an output DC voltage near 400
volts. However, if the RMS AC input voltage is greater than approximately
265 volts, the DC output voltage for a conventional boost converter has to
be increased.
As the DC output voltage increases, the voltage stress on the switching
devices in both the boost converter and the following load converter
increases. This condition requires higher blocking voltage switching
devices. The cost of the higher blocking voltage switching devices is
greater than the lower voltage rated switching devices. Additionally, the
higher voltage rated devices exhibit higher forward conduction voltage
drops and higher switching losses than the lower voltage rated devices,
which makes them more energy-dissipative, and therefore less efficient.
An approach for dealing with this situation is to adopt the buck+boost
topology, which allows the DC output voltage to be lower than the
instantaneous AC input voltage. The DC output voltage may then be
maintained at 400 volts or less even though the peak AC voltage is
greater. There are several disadvantages to the buck+boost converter,
however. First, a large pulsating input current requires a large
electromagnetic interference (EMI) filter to counteract its negative
effects. Also, the buck switch is subjected to both high voltage and high
current stresses. Finally, a large number of silicon devices are typically
required to process the power.
For three-phase rectification, the split-boost converter is a very
efficient topology that allows the DC output voltage to be less than the
peak AC input voltage. The split-boost converter provides two equal output
voltages and requires two separate loads. A basic requirement of this
topology is that the instantaneous rectified AC input voltage must be in a
range that is greater than the individual DC output voltages but less than
twice the individual DC output voltages for the converter to function
properly. As a result, the conventional split-boost topology may not be
used in single-phase, high power factor AC input voltage applications.
Accordingly, what is needed in the art is a way to employ the split-boost
topology for AC input voltages that are less than the individual DC output
voltage.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present
invention provides a split-boost converter having a main inductor, first
and second main switches and floating and fixed outputs and a method of
operating the same. In one embodiment, the converter includes: (1) an
auxiliary diode coupled between the main inductor and a first rail of the
floating output and (2) an auxiliary switch coupled to a node between the
main inductor and the auxiliary diode and a second rail of the floating
output, the converter operable in: (2a) a first mode, realized when an
input voltage of the converter at least equals an output voltage of
(either output of) the converter, in which the auxiliary switch remains
open and the first and second main switches are modulated to operate the
converter and (2b) a second mode, realized when an input voltage of the
converter is less than an output voltage of the converter, in which the
first and second main switches remain closed and the auxiliary switch is
modulated to operate the converter.
Those skilled in the pertinent art understand that a split-boost converter
has a common node and two outputs: one referenced to the common node and
one not referenced to the common node. For purposes of the present
invention, the output referenced to the common node is defined as the
"Fixed" output and the output not referenced to the common node is defined
as the "floating" output.
The present invention therefore provides a split-boost converter that
adapts its operation based on the relationship between its input and
output voltages. In particular, the converter shifts to a mode in which
the auxiliary switch operates the converter when the input voltage is less
than the output voltage. This allows the converter to operate with a
single phase rectifier in which the input voltage provided by the
rectifier regularly drops below the output voltage.
In one embodiment of the present invention, the converter further includes
a first capacitor coupled across the first and second rails of the
floating output. In a related embodiment, the converter further includes a
second capacitor coupled across the first and second rails of the fixed
input.
In one embodiment of the present invention, the converter further includes
a single-phase rectifier coupled to the main inductor. Of course, the
converter may receive its input voltage from a three-phase rectifier or DC
source. If the input voltage drops below the output voltage, the converter
still changes from the first to the second mode of operation.
In one embodiment of the present invention, the converter further includes
a main diode coupled between the second rail of the floating output and a
first rail of the fixed output. Those skilled in the art are familiar with
the operation of such main diodes.
In one embodiment of the present invention, the first mode is realized when
the input voltage at least equals the output voltage of the converter and
at most equals twice the output voltage. This is the case in an embodiment
to be illustrated and described.
In one embodiment of the present invention, the output voltage is between
about 350 volts and about 400 volts DC. In a more specific embodiment, the
output voltage is 400 volts DC.
The foregoing has outlined, rather broadly, preferred and alternative
features of the present invention so that those skilled in the art may
better understand the detailed description of the invention that follows.
Additional features of the invention will be described hereinafter that
form the subject of the claims of the invention. Those skilled in the art
should appreciate that they can readily use the disclosed conception and
specific embodiment as a basis for designing or modifying other structures
for carrying out the same purposes of the present invention. Those skilled
in the art should also realize that such equivalent constructions do not
depart from the spirit and scope of the invention in its broadest form.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, reference is
now made to the following descriptions taken in conjunction with the
accompanying drawings, in which:
FIG. 1 illustrates a prior art split-boost converter;
FIG. 2 illustrates a split-boost converter constructed according to the
principles of the present invention; and
FIG. 3 illustrates a diagram showing an input voltage waveform setting
forth the conditions under which the first and second modes of the
converter of FIG. 2 are selected.
DETAILED DESCRIPTION
Referring initially to FIG. 1, illustrated is a prior art split-boost
converter, generally designated 100. The split-boost converter 100
includes an input rectifier RT having a three phase input voltage Vin, a
main inductor L, a main diode D1, first and second main switches S1, S2
and first and second output capacitors C1, C2, providing first and second
output load voltages V01, V02 respectively. The first and second output
load voltages V01, V02 are substantially equal in value and require two
separate loads.
The first and second main switches S1, S2 are controlled in tandem to open
and close at the same time. When both the first and second main switches
S1, S2 are closed, a voltage difference between the input voltage Vin and
a value equal to one of the first or second load voltages V01, V02 is
applied to the main inductor L causing the main inductor L's current (the
combined load current) to increase. Alternately, when both the first and
second main switches S1, S2 are open, a voltage difference between the sum
of the first and second load voltages V01, V02 and the smaller input
voltage Vin causes the current in the main inductor L to decrease. The
first and second output capacitors C1, C2 provide filtering for the first
and second output load voltages V01, V02 respectively.
The input rectifier RT provides a three phase rectified signal to the main
inductor L. A basic requirement for proper operation of the split-boost
topology is that the rectified input voltage presented to the main
inductor L has a value that is between one and two times the first or
second output load voltage Vo1, Vo2. This condition is easily met with a
three phase rectified input voltage, since the controlling input voltage
phase is always greater than half of the peak voltage value (assuming all
three phases are present). However, for a single phase input voltage this
cannot be achieved, since the rectified input voltage decreases to a zero
value every half cycle.
Turning now to FIG. 2, illustrated is a split-boost converter 200
constructed according to the principles of the present invention. The
split-boost converter 200 includes an input rectifier RT having a single
phase input voltage Vin, a main inductor L, a main diode D1, first and
second main switches S1, S2 and first and second capacitors C1, C2 which
filter a floating output with an output voltage V01 and a fixed output
with an output voltage V02 respectively. The split-boost converter 200
further includes an auxiliary switch Sa and an auxiliary diode Da. The
floating and fixed output voltages V01, V02 are equal in value and require
two separate loads. The floating and fixed output voltages V01, V02 of
each of the floating and fixed outputs is typically between about 350
volts and about 400 volts DC. In the illustrated embodiment, the output
voltage is 400 volts DC.
The split-boost converter 200 includes the single-phase rectifier RT
coupled to the main inductor L. Of course, the split-boost converter 200
may receive its input voltage Vin from a three-phase rectifier
arrangement, which would allow the operation of the split-boost converter
200 to change from a first mode of operation to a second mode if the input
voltage Vin drops below one of the floating and fixed output voltages V01,
V02. In the illustrated embodiment of the present invention, the first
mode is realized when the input voltage Vin at least equals one of the
floating or fixed output voltage V01, V02 of the split-boost converter 200
and at most equals twice the floating and fixed output voltage V01, V02. A
second mode is realized when the input voltage Vin is less than one of the
floating or fixed output voltage V01, V02.
The split-boost converter 200 includes the first capacitor Cl coupled
across first and second rails A, B of the floating output and the second
capacitor C2 coupled across first and second rails D, E of the fixed
output. The split-boost converter 200 further includes a main diode D1
coupled between the second rail B of the floating output and the first
rail D of the fixed output. Those skilled in the art are familiar with the
operation of such main diodes in a split-boost topology.
The present invention therefore illustrates the split-boost converter 200
as having the main inductor L and the first and second main switches S1,
S2 with floating and fixed outputs. As discussed earlier, the split-boost
converter 200 has a common node and two outputs. The fixed output is
referenced to the common node and the floating output is not referenced to
the common node. In the illustrated embodiment, the split-boost converter
200 Includes the auxiliary diode Da coupled between the main inductor L
and the first rail A of the floating output. The auxiliary switch Sa is
coupled to the node C between the main inductor L and the auxiliary diode
Da and the second rail B of the floating output.
The split-boost converter 200 operates in one of the two modes discussed
earlier. The first mode is realized when the input voltage Vin of the
split-boost converter 200 at least equals a floating or fixed output
voltage V01, V02 in which the auxiliary switch Sa remains open and the
first and second main switches S1, S2 are modulated to operate the split
boost converter 200. This is the same mode of operation described in the
split-boost converter 100 of FIG. 1. The second mode is realized when the
input voltage Vin of the split-boost converter 200 is less than the
floating or fixed output voltage V01, V02 in which the first and second
main switches S1, S2 remain closed, thereby placing the two output loads
essentially in parallel, and the auxiliary switch Sa is modulated to
operate the split-boost converter 200 in conjunction with the auxiliary
diode Da. This mode of operation is equivalent to a single-switch boost
converter with the two outputs in parallel, thereby allowing a lower
output voltage than a conventional boost converter would require.
The present invention therefore provides a split-boost converter that
adapts its operation based on the relationship between its input and
output voltages. In particular, the split-boost converter 200 shifts to a
mode in which the auxiliary switch Sa operates the split-boost converter
200 when the input voltage Vin is less than the floating or fixed output
voltage V01, V02. This allows the split-boost converter 200 to operate
with a single phase rectifier in which the voltage provided by the
rectifier RT regularly drops below the floating or fixed output voltage
V01, V02.
Advantages of the illustrated embodiment include operating the split-boost
converter 200 in a continuous current mode (CCM), which is an advantageous
feature of a conventional boost converter as compared to a buck+boost mode
of operation. The output voltage in the illustrated embodiment may be
lower than the peak input voltage, which is not possible with a
conventional boost converter. Also, all of the switching devices are rated
with respect to the floating or fixed output voltage V01, V02, which may
be half that of a conventional boost converter. Additionally, the
volt-second requirement of the main inductor L is smaller than that of a
conventional boost converter, allowing a lower value of inductance to be
used effectively.
Turning now to FIG. 3, illustrated is a diagram showing an input voltage
waveform 300 setting forth the conditions under which the first and second
modes of the split-boost converter 200 of FIG. 2 are selected. The input
voltage waveform 300 shows a repetitive cycle which occurs at the output
of the rectifier RT shown in FIG. 2. The voltage Vo is the value of the
floating or fixed output voltage V01, V02 for the split-boost converter
200 and provides a threshold for switching between the first mode and
second mode of operation discussed in FIG. 2.
When the input voltage waveform 300 is at least equal to the voltage Vo,
The first mode of operation (non-Sa) is realized where the auxiliary
switch Sa is always open and the first and second main switches S1, S2 are
controlling the operation of the split-boost converter 200. When the input
voltage Vin is less than the voltage Vo, the second mode of operation (Sa)
is realized in which the first and second main switches S1, S2 are always
closed and the auxiliary switch Sa is controlling the operation of the
split-boost converter 200.
For a better understanding of conversion technologies and split-boost
converters, see: (1) Y. Jiang and F. C. Lee, "Three Level Boost Converter
for Application in Single-Phase Power Factor Correction", VPEC Power
Electronics Seminar Proceedings, Sep. 11, 1994, pp. 127-133., (2) M. E.
Jacobs, et al., "An Improved High Efficiency Rectifier for Telecom
Applications", Proceedings of INTELEC 1996, pp. 530-535., (3) Y. Jiang and
F. C. Lee, "A New Control Scheme for Buck+Boost Power Factor Control
Circuit", VPEC Power Electronics Seminar Proceedings, Sep. 19, 1993, pp.
189-193 and (4) R. Ridley, et al., "Analysis and Design of a Wide Input
Range Power Factor Correction Circuit for Three-Phase Applications",
Proceedings of APEC, Mar. 7, 1993, pp. 299-305. The aforementioned
references are incorporated herein by reference.
From the above, it is apparent that the present invention provides a
split-boost converter having a main inductor, first and second main
switches and floating and fixed outputs and a method of operating the
same. In one embodiment, the converter includes: (1) an auxiliary diode
coupled between the main inductor and a first rail of the floating output
and (2) an auxiliary switch coupled to a node between the main inductor
and the auxiliary diode and a second rail of the floating output, the
converter operable in: (2a) a first mode, realized when an input voltage
of the converter at least equals an output voltage of (either output of)
the converter, in which the auxiliary switch remains open and the first
and second main switches are modulated to operate the converter and (2b) a
second mode, realized when an input voltage of the converter is less than
an output voltage of the converter, in which the first and second main
switches remain closed and the auxiliary switch is modulated to operate
the converter.
Although the present invention has been described in detail, those skilled
in the art should understand that they can make various changes,
substitutions and alterations herein without departing from the spirit and
scope of the invention in its broadest form.
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